The present application relates to lateral bipolar junction transistor (BJT) structures. More particularly, the present application relates to lateral bipolar junction transistor (BJT) structures containing a wide band gap emitter contact and methods of forming the same.
Heterojunction bipolar junction transistors (HBTs) known in the art include a heterojunction, i.e., a junction of two semiconductor materials having different band gaps, that coincide with a p-n junction between the base and the emitter. The heterojunction at which two different semiconductor materials having different band gaps are joined coincide with the p-n junction. The wider band gap of the emitter relative to the band gap of the base in an HBT increases the current gain relative to a bipolar junction transistor employing a same semiconductor material across the base and the emitter and having similar physical dimensions and doping profiles for the base and emitter.
While the increase in the current gain obtained by an HBT is desirable, the heterojunction between two semiconductor materials having different band gaps may result in a lattice mismatch at the heterojunction. Dislocations are formed in the vicinity of the heterojunction to relieve the stress generated by the lattice mismatch. However, the dislocations in the vicinity of the p-n junction function as scattering centers for charge carriers, reducing the current flow between the emitter and the base. The dislocations may also act as generation and recombination centers, causing an undesirable increase in p-n junction leakage current. Thus, HBTs known in the art may suffer from the deleterious effect of the dislocation centers around the p-n junction despite the advantageous effect of providing a relatively high current gain through formation of the heterojunction between the emitter and the base. In view of the above, there is a need for forming a heterojunction in which dislocation formation is avoided.